Thyroid Endocrinology Flashcards
(25 cards)
What is the process to release thyroid hormone?
- The hypothalamus releases TRH
- The TRH stimulates the anterior pituitary to release TSH
- TSH stimulate the thyroid gland to produce T3 and T4
What are tropic hormones?
Hormones that stimulate other endocrine glands to secrete their hormones
What three hormones does the thyroid gland produce?
- Thyroxine T4
- Triiodothyronine T3
- Calcitonin
Where is the thyroid gland located?
On the lateral surface of the trachea
How is T3 and T4 synthesised?
- Iodide actively trapped into follicle cells
- Iodination of thyroglobulin by thyroperoxidase creates MIT and DIT
- MIT+DIT for T3 and DIT+DIT forms T4
- Stored in colloid then cleaved and released
Which enzyme converts T4 to T3?
5 mono deiodinase
What is the difference between T3 and T4?
T3 is the active form
How is thyroid hormone transported in blood?
Bound to proteins
Which three proteins is thyroid hormone bound to for trasnport?
- Albumin
- Prealbumin
- TBG
What is the feedback mechanism in thyroid hormone regulation?
T4 provides negative feedback to the anterior pituitary to suppress TSH secretion
What are the systemic actions of T3/T4?
- Increase base metabolic rate
- Growth and development
- Maintain normal organ function
What is the calorigenic effect of thyroid hormones?
Increase in oxygen consumption, co2 production and heat generation
What reproductive effects does T4 have?
Essential for normal cycles, breeding seasons and gonadal functions
How does hypothyroid affect protein metabolism?
Decrease protein synthesis
How does hyperthyroid affect protein metabolism?
Increase protein breakdown
How does T4 affect carbohydrate metabolism?
- Increase glucose absorption
- Decrease liver glycogen
How does T4 affect fat metabolism?
- Increase lipolysis
- Increase conversion of cholesterol to bile acids
How does hypothyroid affect the CNS?
- Sluggishness
- Decreased myelin
- Possible permanent damage if young
How does hyperthyroid affect the CNS?
Hypersensitivity
How does T4 affect the cardiovascular system?
Enhances sympathetic effect by increasing adrenergic receptors
How does hyperthyroid affect skeletal muscle?
Decreased efficiency
How does hypothyroid affect skeletal muscle?
Decreased capacity
What causes goitre?
Prolonged TSH stimulation
What are signs of hyperthyroidism?
- Weight loss
- Hyperphagia (need to eat)
- Increase HR and pulse pressure
- Increased heat production
